Comparison of the Surface and Subsurface Oxygen Reactivity and Dynamics with CO Adsorbed on Rh(111)

The translational and angular intensity dependence of CO 2 produced from the reaction of CO with an initial oxygen coverage of 0.5 ML ≤ Θ O ≤ 1.6 ML on Rh(111) at a surface temperature of 450 K was measured. This range of coverages goes from only surface absorbed O to both adsorbed and selvedge absorbed O. The measured CO 2 translational energy is independent of Θ O and is larger than steady-state experiments [ Colonell et al. J. Chem. Phys. 1995, 103, 6677], which were done at lower O coverages, but follows the trend that higher Θ O leads to faster CO 2 . The angular dependence of the intensity is well-described by a sharply peaked function of the form I = a cos n (θ) + (1 – a ) cos(θ), with a = 0.6 and n = 8.6. Again, this was consistent with the previous steady-state results. These observations point to a similar reaction geometry regardless of Θ O; the measured dynamical parameters are independent of whether or not some of the O is subsurface and suggest that absorbed oxygen in the selvedge acts only as a reservoir for replenishing reagent as it is consumed.